Ventriculophasic Reflex

This is part of: Supraventricular Rhythms

Ventriculophasic reflex during second degree AV block type I. The PP interval that follow upon the blocked sinus beat is prolonged.[1]

Ventriculophasic reflex is a phenomenon that can be seen during AV block or during ventricular extrasystoles in bigemini. It describes the sinus arrhythmia that exists during a irregular rhythm. The phenomenon has been described by Erlanger and Blackman in 1910 [2]. Different theories have been postulated to explain the phenomenon (a.o. by Wenkebach), but the theory as published by Rosenbaum and Lepeschkin in 1955 [1] is the most accepted.

A positive chronotropic (accelerating) effect on the ventricular contraction is probably caused by stretch on the right atrium by contraction of the ventricles. A negative chronotropic effect (slows down) is probably caused by a vagal reflex caused by stimulation of the carotic arterial baroreceptors by the pressure wave. The result of these two effects determines whether the P-P interval that surrounds the extra beat is shorter or longer than the P-P interval that surrounds the missing beat.

The baroreflex influences both the sinusnode and the AV node and thus both sinus rate and atrioventricular conduction can be influenced.